Surface modification of plastics, whether of the rigid or flexible type, with fluorine or other halogens has been found to be commercially advantageous in that it is capable of providing, for example, containers having a reduced permeability insofar as liquids having solvent characteristics are concerned and having increased chemical resistance to various liquids and gases which would otherwise react with the unfluorinated container material. One such process and the apparatus therefor is described in U.S. Pat. No. 3,998,180, which is incorporated by reference herein. The disadvantages of this and other halogenation processes having surface modification as an objective are manifold. Some of the processes need a great deal of apparatus because of the steps and conditions imposed by the process, which may entail moving the fluorine, for example, from a holding chamber to a reaction chamber and back again, or the use of very low or high pressures. The more apparatus, of course, the higher the cost factor. Other processes pose a threat to safety. After all, fluorine is a highly toxic, highly corrosive, irritating gas. It is the most reactive element known. Fluorine vigorously reacts with almost all organic and inorganic substances, and because of its highly oxidizing nature, has a fire potential exceeding that of even oxygen. Any process that uses relatively high temperatures, pressures, and/or concentrations of fluorine falls into the hazardous category by increasing the possibility of fire or leakage. Finally, some processes raise the pollution factor because of the amount of fluorine and/or fluorine by-products, such as hydrogen fluoride, which have to be disposed of after the fluorination process is completed. The problems of more apparatus, safety, and pollution are, of course, interrelated because in order to solve the latter problems of safety and pollution, the quantity of apparatus is usually increased and, concommitantly, the investment and operating costs including energy requirements. It is not surprising, then, that industry is constantly striving to decrease the amount of apparatus needed to carry out the surface modification and/or increase the safety factor.